In direct spark ignition engines, fuel is injected directly into each combustion chamber. Accordingly, fuel is not inducted past the intake valve.
The inventors herein have discovered a problem with such engines. Because fuel is not inducted past the intake valve in direct injection spark ignition engines, there is no fuel flow to clean carbon deposits which may deposit on the intake valve. Port injected gasoline engines, on the other hand, induct a mixture of gasoline and air past the intake port. This gasoline mixture cleans carbon deposits which would otherwise accumulate on the intake valve.